Horn array emitter

ABSTRACT

A system and method is disclosed for a parametric emitter array with enhanced emitter-to-air acoustic coupling. The system comprises a plate support member having opposing first and second faces separated by an intermediate plate body. The plate body can have a plurality of conduits configured as an array of acoustic horns. Each horn can have a small throat opening at the first face and an intermediate horn section which diverges to a broad mouth opening at the second face. An emitter membrane can be positioned in direct contact with the first face and extending across the small throat openings. The emitter membrane can be biased by (i) applying tension to the emitter membrane extending across the throat openings, (ii) displacing the emitter membrane into a non-planar configuration, and (iii) capturing the emitter membrane at the first face using an adhesive substance. A variable electrical signal can be applied to the emitter membrane for propagation through the intermediate horn section and out the broad mouth opening at the second face.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

This is a continuation-in-part of U.S. patent application Ser. No.09/819,301 filed on Mar. 27, 2001 which claims priority of United StatesProvisional patent application Ser. No. 60/192,778 filed on Mar. 28,2000.

FIELD OF THE INVENTION

The present invention relates generally to ultrasonic emitters.

BACKGROUND

A variety of emitter devices have been developed which propagateultrasonic energy. These include piezoelectric transducers,electrostatic emitters, mechanical drivers, etc. A challenge with theuse of such devices in air is to provide impedance matching methods toenhance the efficiency of power transfer to the ambient air. Forexample, the wave impedance of a piezoelectric material such as bariumtitanate exceeds the impedance of air by a factor of 105. This extremeimpedance difference severely attenuates transmission of a propagatedultrasonic beam of energy into the air.

The use of acoustic horns as transformer devices is well known withrespect to most sound systems for both audio and ultrasound frequencies.Extensive research has been done detailing preferred horn configurationsfor specific frequency ranges. Mathematical formulas are generallyavailable to optimize the geometry of each application for a givenfrequency.

A publication by Fletcher and Thwaites entitled “Multi-horn MatchingPlate for Ultrasonic Transducers” Ultrasonics 1992, Vol 30, No. 2,discloses the use of an array of acoustic horns formed in a plate as anacoustic transformer for ultrasonic transmission into air. Based on thisdisclosure, FIG. 1 shows a transducer aligned with a horn plate. Aspacing gap between the emitter element and throats of the respectivehorns is illustrated and identified as a key element in optimizing theefficiency of the horn array for ultrasonic energy. By choosing a gapdistance specifically selected for a given horn array, the publicationsuggests improvement of pressure gain in transducer output by 10 dB orbetter.

Despite enhancement of the effectiveness by this horn array system,there remain significant problems in impedance matching, particularlywith ultrasonic emitters.

Many new applications of ultrasonic energy, including parametricspeakers, are offering new opportunities which require high levels ofefficiency in order to obtain a commercially acceptable audio outputfrom ultrasonic emissions. Generally, these parametric applicationsdepend on effective impedance matching to enable propagation ofultrasonic waves into the air as the nonlinear medium necessary foracoustic heterodyning.

SUMMARY

A system and method is disclosed for a parametric emitter array withenhanced emitter-to-air acoustic coupling. The system comprises a platesupport member having opposing first and second faces separated by anintermediate plate body. The plate body can have a plurality of conduitsconfigured as an array of acoustic horns. Each horn can have a smallthroat opening at the first face and an intermediate horn section whichdiverges to a broad mouth opening at the second face. An emittermembrane can be positioned in direct contact with the first face andextending across the small throat openings. The emitter membrane can bebiased by (i) applying tension to the membrane extending across thethroat openings, (ii) displacing the membrane into a non-planarconfiguration, and (iii) capturing the emitter membrane at the firstface using an adhesive substance. A variable electrical signal can beapplied to the membrane for propagation through the intermediate hornsection and out the broad mouth opening at the second face.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention; and, wherein:

FIG. 1 depicts a prior art example of an emitter configuration utilizingan array of horn transformers for acoustic coupling with air;

FIG. 2 shows a perspective view of an integral emitter/horn arrayconstructed in accordance with an embodiment of the present invention;

FIG. 3 is a detailed sectional view of the integral emitter and throatof the horn in accordance with an embodiment of the present invention;

FIGS. 4 through 6 graphically illustrate alternative embodimentsdemonstrating various methods of displacing the emitter membrane withinthe small throat opening in accordance with an embodiment of the presentinvention;

FIG. 7 a shows an elevational view of an integral emitter/horn arrayhaving elongate impedance transformer strips in accordance with anembodiment of the present invention;

FIG. 7 b shows an elevational view of the emitter/horn array of FIG. 9 ain an exploded view in accordance with an embodiment of the invention;

FIG. 8 graphically illustrates an embodiment of a horn array as part ofa parametric speaker system for generating audio frequencies fromultrasonic output;

FIG. 9 illustrates a flow chart depicting a method for developing a highefficiency acoustic coupling device for coupling parametric emitters toa surrounding air environment in accordance with an embodiment of thepresent invention; and

FIG. 10 illustrates a flow chart depicting a method for enhancingemitter-to-air acoustic coupling of a parametric array in accordancewith an embodiment of the present invention.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

A parametric emitter array 10 is illustrated in FIG. 2. It comprises aplate support member 11 having opposing first and second faces 13 and 12separated by an intermediate plate body 14. The plate 11 is preferably arigid material (metal, ceramic, polymer, etc), and may be eitherconductive or nonconductive, depending on the method of driving anemitter membrane 20 directly coupled to the first face 13. The thicknessof the plate may vary, depending on the acoustic coupling propertiesrequired for specific frequency ranges and particular applications.Generally, the plate thickness will be within the range of 1 millimeter(mm) to 20 mm. The selection of acoustical, electrical and physicalproperties will be discussed hereafter.

The plate body includes a plurality of conduits configured as an arrayof acoustic horns 30. Each horn has a small throat opening 31 at thefirst face 13 and an intermediate horn section 32 which diverges to abroad mouth opening 33 at the second face 12. The degree of flair in theintermediate horn section, as well as the size of the respective smallthroat and broad mouth openings 31 and 33 may be configured inaccordance with conventional design parameters. These parameters will bebalanced and optimized, depending upon the degree of directionalitydesired, the bandwidth response selected and the gain and couplingefficiency intended. Detailed design considerations are therefore deemedunnecessary for enablement of the present disclosure. Representativedimensions illustrated in FIG. 2 are a 10 mm diameter for the mouth 33,2 mm diameter for the throat opening, and 10 mm for length or thicknessof the plate.

In the illustrated embodiment, the array of horns comprises conduitswhich are molded to a desired shape within the plate support member foracoustic coupling of ultrasonic frequencies to surrounding air.Appropriate techniques are well known within the injection moldingindustry for implementing these procedures. Alternatively, the array ofhorns may have conduits which are machined to the desired shape.

One embodiment of the plate support member comprises a circular plate asopposed to the rectangular shape illustrated in FIG. 2. Such aconfiguration offers an emitted sound column of more uniform naturebecause of the common radius of the resulting beam output. Dimensions ofthe plate support member may vary. However, the diameter the diameter ofthe plate support member is generally at least three inches. Theconfiguration may be planar or curved. A concave configuration enablesselection of a curvature radius to minimize phase misalignment for alistener location at a predetermined distance from the emitter array.This is accomplished by adjusting the radius of curvature of theemitting face so that the distances from each mouth opening are commonat a given listener location. Numerous other variations will be apparentto those of ordinary skill in the art.

Many forms of acoustic emitters may be coupled directly to the opening31 at the throat of the horn. Selection of a specific emitter will be afunction of the intended use of the horn array. Generally these emittersfall within two classes. The first class of emitters comprises thosewhich function as the primary source of mechanical movement fordevelopment of compression waves. This class, referred to as acousticdrivers, includes an emitter membrane which is mechanically orphysically displaced to create periodic compression waves in a direct oractive mode. Examples of the first class of drivers includespiezoelectric emitters, mechanical oscillators, and similar structureswhich displace in response to energy supplied directly to the membrane.

One example embodiment conceived as part of the present inventioninvolves the use a film or flexible membrane. Various types of film maybe used as an emitter film. The important criteria are that the film becapable of (i) deforming into arcuate emitter sections at the opening 31locations, and (ii) responding to an applied electrical signal toconstrict and extend in a manner that reproduces an acoustic outputcorresponding to the signal content. Although piezoelectric materialsare the primary materials that supply these design elements, newpolymers are being developed that are technically not piezoelectric innature. Nevertheless, the polymers are electrically sensitive andmechanically responsive in a manner similar to the traditionalpiezoelectric compositions. Accordingly, it should be understood thatreference to piezoelectric films in this application is intended toextend to any suitable film that is both electrically sensitive andmechanically responsive (ESMR) so that acoustic waves can be realized inthe subject transducer.

One type of ESMR film is made of polyvinylidene difluoride (PVDF)material. This material has demonstrated surprising utility with respectto direct generation of ultrasonic emissions as will be discussedhereafter. Because PVDF material responds directly to voltagevariations, ultrasonic emissions can be directly generated at the smallthroat opening in a highly controlled manner by applying a variableelectrical signal at a frequency proportional to the desired sonic orultrasonic emission frequency or combination of frequencies.

The second class of emitters is characterized by passive or indirectpower transmission, rather than in an active or direct mode.Electrostatic and magnetostrictive emitters are representative of thisgroup. Operation of these emitters requires an independent drive sourcesuch as a variable voltage back plate or some other driver whichpassively or indirectly displaces the emitter mounted at the throatopening 31. For example, an electrostatic membrane having a conductivefilm may be directly coupled at the small opening 31, and pinched orotherwise biased into a state of tension. Variable electronic signalsoperated at a sonic or ultrasonic frequency or combination offrequencies can be applied to a conductive back plate which iselectrically insulated from the membrane film, thereby coupling theultrasonic signal to the electrostatic membrane for generating thedesired compression waves through the horn.

Both classes of emitters are positioned in direct contact with the firstface 13 and extend across the small throat openings. This is somewhatcounter to teachings of the prior art, which have required adisplacement gap between the emitter and the small opening of the horn.The present inventors have discovered that by directly attaching theemitter at the first face 13, and in direct position at the throat ofthe horn, enables the horn to be a highly efficient ultrasonic emissionsource which couples surprisingly well with a surrounding airenvironment.

A biasing means is required for enabling the emitter membrane toproperly function. This biasing means may be physically or inductivelyoperative with respect to the emitter membrane. The biasing means iscapable of (i) applying tension to the membrane extending across thethroat openings and (ii) displacing the membrane into a non-planarconfiguration. This is represented in FIG. 3 et. seq. by the slightlydeformed or displaced emitter membrane 35 which is projecting within thesmall throat opening 31. The emitter membrane is part of a continuousmembrane 20 which is disposed across the first face 13 of the platesupport member. For example, the deformed emitter membrane 35 may be apreformed dimple positioned within the continuous membrane 20 and inalignment with the small throat opening 31. The dimpled structure formspart of the biasing means as described above, and would be complementedwith a tension force to place the emitter membrane in a biased positionwhich permits vibrating motion consonant with a desired sonic orultrasonic signal.

The ESMR film may be captured at the film contacting faces using anadhesive substance to provide a substantially permanent tension force tothe film. The film may be deformed into a non-planar configuration priorto being captured. An electrically conducting adhesive can be used sothat the film contacting face may also serve as an electrode to transfera voltage applied to the support member to the ESMR film. When highlevels of voltage are applied to an ESMR film, the film may generateheat that should be dissipated. Hence, there may be a preference thatthe adhesive be thermally conductive, so that the support member mayalso serve as a heat sink for the ESMR film. Finally, to ease themanufacturing process, and to improve the reliability of the transducer,there also may be a preference that the adhesive have a rapid cure time,facilitated when an accelerating or activating fluid is applied. Whenthe adhesive material is applied to the film contacting face, it isimportant to apply the adhesive as uniformly as possible.Inconsistencies in the adhesives or film contacts may result ininconsistencies in the arcuate sections of the film, causing a lower Q,and unwanted distortion. A screen-printing technique may be used touniformly apply the adhesive. It may be preferred that the thickness ofthe adhesive be less than ten thousandths of an inch.

The ESMR film can also be coupled to a back plate 40 using electricallyconductive adhesive material. The backplate can be positioned behind themembrane and adjacent the small throat openings, and may also serve aspart of the biasing means. For example, corresponding dimples 41 can beformed on the back plate in proper alignment to force the emittermembrane within the small throat openings 31. A spacer element 43 may beinserted between the back plate 40 and the emitter membrane 20 todisplace the emitter portion 35 from contact with the back plate 40.This may be enhanced by the capture of a pocket of air 45 as a cushionwhich provides displacement space for the emitter membrane 35. WhereESMR film comprises the emitter membrane, vibration displacementsactivated by a variable voltage source can be of such small distancesthat the gap formed by the pocket of air 45 may be very small.

The spacer element 43 may also be viewed as structure for clamping themembrane in fixed position around the small throat opening such thatvibrational energy is not transferred through the membrane to adjacenthorns. This same function can be performed by the back plate in theabsence of the spacer element. Isolation of each emitter element 35 isimportant for minimizing cross transmission of vibrations through thecontinuous membrane 20. The spacer and/or back plate can also act as adamping member to reduce vibrations carried through the plate supportmember 11 (FIG. 1). With each emitter membrane being supplied by acommon voltage or energy source, and operating as a continuous membranehaving uniform physical properties, the isolated emitter sections 35 canbe tuned and electronically or mechanically activated to develop auniform wave front with minimal distortion. The application of thisemitter configuration with an array of horn-type acoustic transformersoffers significant advantages over other emitter systems.

The back plate, as shown in FIG. 3, may also include protrudingstructure 41 aligned with each small throat opening as part of thebiasing means. The protruding member operates to displace the emittermembrane slightly and/or to apply proper tension with sufficientdisplacement to allow activation as a sonic or ultrasonic generator.Again, where ESMR film is used, the displacement distance is so nominalthat the protruding portion need not extend more than 3 mm. FIGS. 3-6illustrate various geometric shapes that are useful to displace theemitter membrane into the desired non-planar configuration.

The protruding structure 41 shown in FIG. 3 comprises a convex bumphaving a size approximately equal to the small throat opening such thatthe bump projects within the throat of the horn. This configuration isvery effective in isolating and developing uniform vibration responseacross the emitter section. The back plate includes means for developinga gap between the convex bump and the membrane to allow vibrationaldisplacement of the membrane when activated with a sonic or ultrasonicfrequency, thereby avoiding distorting contact with the convex bump.Typical dimensions of the convex bump include a radius of curvature of10-30 mm and a height of 1-3 mm from the planar surface of thebackplate.

An additional method for developing the required gap between the convexbump and the membrane comprises structure for supplying an electrostaticcharge operable to repel the membrane from the bump during operation.This can be accomplished by establishing a baseline signal within theESMR film which maintains a threshold tension, enabling the desiredoutput signal to be applied for the generation of the sonic output inthe emitter. It is possible to utilize a carrier signal for this biasingpurpose, with sidebands providing the output signal. A similar biasingmeans can be developed with structure for supplying a magnetic forceoperable in a manner similar to the electrostatic embodiment to repelthe membrane from the bump during operation.

As indicated above, a simple means for developing the required gapbetween the convex bump and the membrane may consist of a spacer ringpositioned between the membrane and the back plate, with the bump beingdisposed in alignment with a central opening of the spacer ring. Thisspacer element is representative of numerous forms of mechanical meansuseful for displacing the emitter membrane from the backplate and bump.The thickness of the spacer will depend upon the range of frequency andamplitude of vibration of the emitter member. Typically, when operatingwithin the ultrasonic range, spacer elements will vary in dimension from1 to 3 mm. Numerous materials may be selected, balancing such factors asinsulative properties, damping constants, expansion coefficients, andchemical/mechanical compatibility with the backplate and the supportplate.

Other forms of mechanical means for developing the gap between the backplate and the membrane are represented in FIGS. 4 to 6. These include aprotruding structure having an apex configuration in contact with acentral portion of the membrane to physically displace the membrane fromthe back plate. As an example, FIG. 4 shows a conical structure 61having an apex 62 in contact with a central portion of the membrane 63to physically displace the membrane. A further embodiment shown in FIG.5 comprises a pin structure 71 having an apex 72 in contact with acentral portion of the membrane 73. These embodiments may be providedwith a spacer 43 to develop the desired gap between the back plate andmembrane. The various shapes are to be considered as representative ofthe general concept that the emitter membrane can be mechanicallydisplaced to provide the biasing and necessary gap for operation withinthe inventive concept.

FIG. 6 illustrates the placement of the projecting element directly fromthe back plate without presence of a spacer for gap formation. Instead,a small projection 81 extends at a sufficient length to displace themembrane 83 away from the back plate 40 to provide space for vibration.With minimal displacements such as occur with higher ultrasonicfrequencies, small gaps 84 on each side of the projection 81 aresufficient to enable operation of the emitter.

Another embodiment of a horn array emitter comprising a rectangularemitter 700 is shown in FIG. 7 a. A plate support member 712 can haveopposing first 702 and second 706 faces. The plate support emitter canhave a first dimension 724 that is longer than a second dimension 734.The plate support emitter may be formed having a plurality of channels708. In one embodiment, the channels can run a length of the plate. Theplate support member can be a rigid material (metal, ceramic, polymer,etc), and may be either conductive or nonconductive. An emitter membrane710 can be placed over the first face of the plate support member andchannels. The emitter membrane can be an ESMR film. The emitter membranecan be coupled to the first face in such a way that the film forms aconcave or convex surface over each channel. Elongate impedancetransformer strips 704 can be located between each channel and placedabove the emitter membrane. Each impedance transformer strip can have awidth sufficient to enable each side of the strip to extend over aportion of a channel such that there is an opening of a predeterminedwidth between the strips above each channel. The strips can be shaped toprovide a rectangular shaped flared opening. The flared opening can havean exponential flare, or some other shape configured to reduce theimpedance mismatch between the emitter membrane and the medium in whichthe film is located. The opening can form an elongated exponential hornwhich can enable acoustic waves from the emitter membrane to haveimproved impedance matching with the air surrounding the horn arrayemitter. The actual dimensions of the opening and shape of thetransformer strips can be determined using conventional designconsiderations. A support 716 can be used to provide added stability tothe rectangular emitter 700.

The emitter membrane 710 can be physically displaced to provide periodicdisplacement waves. The rectangular shape of the emitter can enable thedisplacement waves to be substantially directional in the long dimensionof the emitter, while allowing the waves to spread in the directionperpendicular to the long dimension. When the emitter is used to produceparametric sound, it can be advantageous to provide directionality inonly one dimension. For example, when the emitter is used to produceparametric sound in an exhibit such as a museum, the sound can bedirected within the confines of a beam of predetermined beam width inthe long direction of the speaker. This can confine the sound to beconfined to a narrow area of an exhibit room. However, allowing thesound to spread in the narrow dimension of the emitter enables the soundto be heard over a wide variety of heights. This enables confinement ofthe sound while allowing short and tall exhibit participants to hear thesound substantially equally. Thus, the rectangular shape of the emittercan be beneficial.

An exploded view of the rectangular emitter 700 is shown in FIG. 7 b. Afirst portion 750 is shown comprising the elongate impedance transformerstrips 704 coupled to a plurality of supports 716. The transformerstrips can be formed using any standard plastic injection or millingprocess. The strips can be formed from a substantially rigid materialsuch as metal, plastic, composite, or wood. The material from which thestrips are formed can be selected for its ability to impedance match theemitter membrane 710 with the surrounding medium (typically air). Asecond portion 760 is shown comprising the plate 712 used to carry theemitter membrane. The first portion can be coupled to the second portionto form the rectangular emitter.

The present invention offers utility in many areas of parametric wavegeneration. One embodiment of the present invention utilizes aparametric or heterodyning technology, which is particularly adapted forthe present thin film structure. The thin electrostatic film of thepresent invention is well suited for operation at high ultrasonicfrequencies in accordance with parametric speaker theory. It isparticularly useful in coupling ultrasonic output to surrounding air.The efficiency of this system is most evident with respect toapplications with parametric speaker systems where the signal source iscoupled to an amplitude modulator for mixing audio frequencies withultrasonic frequencies to develop an ultrasonic wave form with at leastone sideband corresponding to the audio frequencies. The horn array canenable the combined carrier and sideband compression waves to be moreefficiently propagated within the surrounding air environment. Due tothe non-linear effects of air, the combined carrier and sidebandcompression wave can produce sum and difference frequencies between thecarrier and sideband waves within the air environment. The resultingdifference frequencies can comprise the original audio frequencies togenerate audio output as part of an acoustic heterodyne speaker system.Such a system is illustrated in FIG. 8.

The parametric speaker 142 includes a typical circuit 146 in which amodulator 150 is coupled to an ultrasonic frequency generator 154 and asonic (or subsonic) input 158. The sonic or sub-sonic input can includea digital audio source, an analog audio source, a pre-recorded audiosource, or a live audio source such as a microphone. The ultrasonicfrequency generator 154 can be an oscillator or a digital ultrasonicwave source. The generator can produce a carrier signal, or firstultrasonic signal f₁ 159. The modulator 150 operates to produce a secondultrasonic signal f₂ 157 having a frequency difference from the firstultrasonic signal 159 such that the modulated output, or secondultrasonic frequency f₂ 157, comprises the sum or difference of thesonic input 158 and the first ultrasonic signal f₁ 159. The first andsecond ultrasonic signals can be combined 161 to produce an ultrasonicparametric signal 162 such that the sonic input 158 can be decoupledfrom the ultrasonic parametric signal 162 when the parametric signal isproduced within a nonlinear medium such as air.

For example, the sonic input 158 can be a 5 kHz sonic signal. Theultrasonic frequency generator 154 can produce a 40 kHz ultrasonicsignal as a first ultrasonic signal, f₁ 159. The sonic signal and thefirst ultrasonic signal 159 can be modulated, or sent through anon-linear circuit such as a mixer 150. The mixer can include a filterto yield a single sideband output of the first ultrasonic signal that iseither a sum, 45 kHz, or a difference, 35 kHz, of the first ultrasonicand sonic signals. In this example it will be assumed that the mixerwill output the sum, 45 kHz. The output of the single side band mixer f₂161 can then be summed 157 with the first ultrasonic signal 159 f₁ tocreate an ultrasonic parametric signal 162 comprising both the 45 kHzsignal output from the mixer and the 40 kHz first ultrasonic signal. Theultrasonic parametric signal 162 can then be emitted by the parametricspeaker 142 into a non-linear medium such as air.

At least one embodiment of the present invention is able to function asdescribed because the ultrasonic signals corresponding to f1 and f2interfere in air according to the principles of acoustical heterodyning.Acoustical heterodyning is somewhat of a mechanical counterpart to theelectrical heterodyning effect which takes place in a non-linearcircuit. For example, amplitude modulation in an electrical circuit is aheterodyning process. The heterodyne process itself is simply thecreation of two new waves. The new waves are the sum and the differenceof two fundamental waves.

In acoustical heterodyning, the new waves equaling the sum anddifference of the fundamental waves are observed to occur when at leasttwo ultrasonic compression waves interact or interfere in air. Thepreferred transmission medium of the present invention is air because itis a highly compressible medium that responds non-linearly underdifferent conditions. This non-linearity of air enables the heterodyningprocess to take place, decoupling the difference signal from theultrasonic output. However, it should be remembered that anycompressible fluid can function as the transmission medium if desired.

In the present example, the non-linear medium of air can cause a sumsignal of the 45 kHz signal and the 40 kHz signal to create an 85 kHzsignal, and a difference signal of 5 kHz. The 85 kHz signal is wellabove the human hearing range of 20 kHz and will not be noticed. Thus,the 5 kHz sonic signal is the only frequency which can be heard by alistener.

Whereas successful generation of a parametric difference wave in theprior art appears to have had only nominal volume, the presentconfiguration can generate full sound. This full sound is enhanced toimpressive volume levels because of the significant increase in couplingefficiency between the emitter diaphragm and the surrounding air.

The development of full volume capacity in a parametric speaker providessignificant advantages over conventional speaker systems. Most importantis the fact that sound is reproduced from a relatively masslessradiating element. Specifically, there is no radiating element operatingwithin the audio range because the film is vibrating at ultrasonicfrequencies. This feature of sound generation by acoustical heterodyningcan substantially eliminate distortion effects, most of which are causedby the radiating element of a conventional speaker. For example, adverseharmonics and standing waves on the loudspeaker cone, cone overshoot andcone undershoot are substantially eliminated because the low mass, thinfilm is traversing distances in millimeters.

It should also be apparent from the description above that the preferredand alternative embodiments can emit sonic frequencies directly, withouthaving to resort to the acoustical heterodyning process describedearlier. However, the greatest advantages of the present invention arerealized when the invention is used to generate the entire range ofaudible frequencies indirectly using acoustical heterodyning asexplained above.

From a procedural perspective, the present invention may be viewed as amethod 900 for developing a high efficiency acoustic coupling device forcoupling parametric emitters to a surrounding air environment, as shownin the flow chart of FIG. 9. The method can include he steps of: a)integrally attaching an emitter membrane at a small throat opening of anacoustic horn, as shown in block 910; b) applying sonic frequencies tothe emitter membrane to generate sonic compression waves at the smallthroat opening of the acoustic horn, as shown in block 920; and c)propagating the sonic compression wave through the acoustic horn forenhanced air coupling at a broad mouth of the horn, as shown in block930.

A further embodiment of the present invention includes a method 1000 fordeveloping a high efficiency acoustic coupling device for couplingparametric emitters to a surrounding air environment, as shown in theflow chart of FIG. 10. The method can include the operation of formingan array of acoustic horns by preparing a plate support member havingopposing first and second faces separated by an intermediate plate body,said plate body having a plurality of conduits configured as an array ofacoustic horns, each horn having a small throat opening at the firstface and an intermediate horn section which diverges to a broad mouthopening at the second face, as shown in block 1010. A further operationinvolves attaching an emitter membrane at a small throat opening of anacoustic horn, as shown in block 1020. Another operation includesbiasing the emitter membrane by (i) applying tension to the emittermembrane extending across the throat openings, (ii) displacing theemitter membrane into a non-planar configuration, and (iii) capturingthe emitter membrane at the first face using an adhesive substance, asshown in block 1030. A further operation involves applying a variableelectrical signal to the emitter membrane for propagation through theintermediate horn section and out the broad mouth opening at the secondface, as shown in block 1040.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

1. A parametric emitter array with enhanced emitter-to-air acousticcoupling, said emitter comprising: a plate support member havingopposing first and second faces separated by an intermediate plate body,said plate body having a plurality of conduits configured as an array ofacoustic horns, each horn having a small throat opening at the firstface and an intermediate horn section which diverges to a broad mouthopening at the second face; an emitter membrane positioned in directcontact with the first face and extending across the small throatopenings; wherein the emitter membrane is biased by (i) applying tensionto the membrane extending across the small throat openings, (ii)displacing the membrane into a non-planar configuration, and (iii)capturing the emitter membrane at the first face using an adhesivesubstance; and a variable electrical signal applied to the emittermembrane for propagation of compression waves through the intermediatehorn section and out the broad mouth opening at the second face.
 2. Aparametric emitter array as defined in claim 1, further comprising aback plate positioned behind the emitter membrane and adjacent the smallthroat openings, said back plate including contact structure forclamping the emitter membrane in fixed position around the small throatopening such that vibrational energy is not transferred through theemitter membrane to adjacent horns.
 3. A parametric emitter array asdefined in claim 2, wherein the back plate includes protruding structurealigned with each small throat opening, said protruding structureenabling the emitter membrane to be displaced into the non-planarconfiguration.
 4. A parametric emitter array as defined in claim 3,wherein the protruding structure comprises a convex bump having a sizeapproximately equal to the small throat opening, said back plateincluding means for developing a gap between the convex bump and theemitter membrane to allow vibrational displacement of the emittermembrane when activated with the variable electrical signal withoutcontact with the convex bump.
 5. A parametric emitter array as definedin claim 4, wherein the means for developing the gap between the convexbump and the emitter membrane comprises structure for supplying anelectrostatic charge operable to repel the emitter membrane from theconvex bump during operation.
 6. A parametric emitter array as definedin claim 4, wherein the means for developing the gap between the convexbump and the emitter membrane comprises structure for supplying adifferential air pressure operable to maintain the gap during operation.7. A parametric emitter array as defined in claim 4, wherein the meansfor developing the gap between the convex bump and the emitter membranecomprises structure for supplying a magnetic force operable to repel theemitter membrane from the convex bump during operation.
 8. A parametricemitter array as defined in claim 4, wherein the means for developingthe gap between the convex bump and the emitter membrane comprises aspacer ring positioned between the emitter membrane and the back plate,said convex bump being disposed in alignment with a central opening ofthe spacer ring.
 9. A parametric emitter array as defined in claim 4,wherein the means for developing the gap between the back plate and theemitter membrane comprises protruding structure having an apex incontact with a central portion of the emitter membrane to physicallydisplace the emitter membrane from the back plate during operation, saidcontact of the apex with the emitter membrane being sufficiently nominalto allow transfer of the variable electrical signal to the membrane asan emitter.
 10. A parametric emitter array as defined in claim 3,wherein the protruding structure comprises a conical structure having anapex in contact with a central portion of the emitter membrane tophysically displace the emitter membrane from the back plate duringoperation, said contact of the apex with the emitter membrane beingsufficient to allow transfer of the variable electrical signal to themembrane as an emitter.
 11. A parametric emitter array as defined inclaim 3, wherein the protruding structure comprises a pin structurehaving an apex in contact with a central portion of the emitter membraneto physically displace the emitter membrane from the back plate duringoperation, said contact of the apex with the emitter membrane beingsufficient to allow transfer of the variable electrical signal to themembrane as an emitter.
 12. A parametric emitter array as defined inclaim 1, wherein the emitter membrane is further biased by anelectrostatic charge applied to the emitter membrane, the electrostaticcharge being configured to displace the emitter membrane from the firstface.
 13. A parametric emitter array as defined in claim 1, wherein saidplate support member is comprised of an electrically conductive materialwhich is capable of carrying a voltage for supplying the variableelectrical signal to the emitter membrane.
 14. A parametric emitterarray as defined in claim 1, wherein the emitter membrane comprises anESMR film responsive to voltage changes to generate physical vibrationsat the small throat opening as an emitter.
 15. A parametric emitterarray as defined in claim 14, wherein the ESMR film is comprised of aPVDF material.
 16. A parametric emitter array as defined in claim 14,wherein the variable electrical signal applied to the emitter membranecomprises a voltage signal source coupled to the emitter membrane andoperable to supply the variable electrical signal which is converted bythe ESMR film of the emitter membrane into the compression waves.
 17. Aparametric emitter array as defined in claim 16, wherein the voltagesignal source comprises an ultrasonic signal generator which is coupledto an amplitude modulator for mixing audio frequencies with ultrasonicfrequencies to develop an ultrasonic wave form having at least onesideband corresponding to the audio frequencies, said sonic emitterproviding ultrasonic compression waves propagating from the horn arraywithin a surrounding air environment which decouples the audiofrequencies to generate audio output as part of an acoustic heterodynespeaker system.
 18. A parametric emitter array as defined in claim 2,wherein the emitter membrane comprises a dielectric material responsiveto electrostatic voltage changes to generate physical vibrations at thesmall throat opening as an electrostatic sonic emitter, said back platecomprising a conductive medium capable of driving the electrostaticemitter at the sonic frequencies.
 19. A parametric emitter array asdefined in claim 18, wherein the variable electrical signal applied tothe emitter membrane comprises a voltage signal source coupled to theback plate and operable to supply a variable signal which is convertedby the dielectric material of the emitter membrane into the compressionwaves.
 20. A parametric emitter array as defined in claim 19, whereinthe variable electrical signal comprises an ultrasonic signal generatorwhich is coupled to an amplitude modulator for mixing audio frequencieswith ultrasonic frequencies to develop an ultrasonic wave form having atleast one sideband corresponding to the audio frequencies, saidparametric emitter providing ultrasonic compression waves propagatingfrom the horn array within a surrounding air environment which decouplesthe audio frequencies to generate audio output as part of an acousticheterodyne speaker system.
 21. A parametric emitter array as defined inclaim 1, wherein the plate support member comprises a circular plate.22. A parametric emitter array as defined in claim 1, wherein platesupport member includes an emitter array having a diameter of at leastthree inches.
 23. A parametric emitter array as defined in claim 21,wherein the circular plate is planar in configuration.
 24. A parametricemitter array as defined in claim 21, wherein the circular plate isconcave in configuration, having a radius of curvature selected tominimize phase misalignment at a listener location at a predetermineddistance from the emitter array.
 25. A parametric emitter array asdefined in claim 1, wherein the array of horns comprises conduits whichare molded to a desired shape within the plate support member foracoustic coupling of ultrasonic frequencies to surrounding air.
 26. Aparametric emitter array as defined in claim 1, wherein the array ofhorns comprises conduits which are machined to a desired shape withinthe plate support member for acoustic coupling of ultrasonic frequenciesto surrounding air.
 27. A parametric emitter array as defined in claim1, wherein the emitter membrane is preformed with an array of dimplespositioned for alignment with the small throat openings of the hornarray to provide the non-planar configuration.
 28. A parametric emitterarray as defined in claim 27, wherein the array of dimples are uniformin size and acoustic response to generate a substantially common wavefront at the second face of the plate support member.
 29. A parametricemitter array as defined in claim 1, wherein the adhesive substance isapplied to the emitter membrane to enable the emitter membrane to becaptured at the first face.
 30. A parametric emitter array as defined inclaim 1, wherein the adhesive substance is applied to the emittermembrane to form a substantially uniform layer of adhesive on theemitter membrane by applying the adhesive to the emitter membrane usinga screen printing technique.
 31. A parametric emitter array as definedin claim 30, wherein the substantially uniform layer of adhesive on theemitter membrane has an average thickness of less than less than tenthousandths of an inch.
 32. A parametric emitter array as defined inclaim 1, wherein the variable electrical signal varies at one of anultrasonic frequency and a sonic frequency.
 33. A parametric emitterarray as defined in claim 1, wherein the variable electrical signalvaries at two or more frequencies.
 34. A parametric emitter array asdefined in claim 1, wherein the array of acoustic horns furthercomprises a plurality of elongate impedance transformer stripsconfigured to reduce an impedance mismatch between the emitter membraneand the air.
 35. A parametric emitter array as defined in claim 34,further comprising a plate having a plurality of substantially parallelchannels.
 36. A parametric emitter array as defined in claim 35, whereinthe emitter membrane is coupled to the plate support member over theparallel channels.
 37. A parametric emitter array as defined in claim36, wherein the emitter membrane is coupled to the plate support memberin such a way that the emitter membrane forms one of a concave and aconvex surface over at least one channel.
 38. A parametric emitter arrayas defined in claim 34, wherein at least one of the plurality ofelongate impedance transformer strips is configured to provide arectangular shaped exponential opening adjacent to the parallelchannels.
 39. A parametric emitter array as defined in claim 34, whereinthe plurality of elongate impedance transformer strips have a lengthsufficient to enable the parametric emitter array to have a rectangularshape, wherein the rectangular shaped parametric emitter array enablesdirectional sound to be produced in one dimension of the array.
 40. Amethod for developing a high efficiency acoustic coupling device forcoupling parametric emitters to a surrounding air environment, saidmethod comprising the steps of: a) attaching an emitter membrane at asmall throat opening of an acoustic horn; b) applying a variableelectrical signal to the emitter membrane to generate compression wavesat the small throat opening of the acoustic horn; and c) propagating thecompression waves through the acoustic horn for enhanced air coupling ata broad mouth of the horn.
 41. A method as defined in claim 40, furthercomprising the steps of: forming an array of acoustic horns by preparinga plate support member having opposing first and second faces separatedby an intermediate plate body, said plate body having a plurality ofconduits configured as an array of acoustic horns, each horn having asmall throat opening at the first face and an intermediate horn sectionwhich diverges to a broad mouth opening at the second face; positioningan emitter membrane in direct contact with the first face and extendingacross the small throat openings; biasing the emitter membrane by (i)applying tension to the emitter membrane extending across the smallthroat openings, (ii) displacing the emitter membrane into a non-planarconfiguration, and (iii) capturing the emitter membrane at the firstface using an adhesive substance; and applying a variable electricalsignal to the emitter membrane for propagation through the intermediatehorn section and out the broad mouth opening at the second face.
 42. Amethod as defined in claim 41, wherein the biasing step is accomplishedin part by coupling a back plate against the emitter membrane to pinchthe emitter membrane at the small throat opening and isolating theemitter membrane from adjacent acoustic horns within the plate supportmember.
 43. A method as defined in claim 41, wherein the emittermembrane performs the additional step of actively generating compressionwaves within the acoustic horn.
 44. A parametric emitter array withenhanced emitter-to-air acoustic coupling, said emitter comprising: aplate support member having opposing first and second faces, the firstface having a plurality of substantially parallel channels; an emittermembrane coupled to the first side of the plate support member over theplurality of substantially parallel channels; and at least two elongateimpedance transformer strip configured to provide a rectangular shapedflared opening adjacent to the parallel channels.
 45. A parametricemitter array as defined in claim 44, wherein the emitter membrane isbiased by (i) applying tension to the membrane extending across theplurality of channels, (ii) displacing the membrane into a non-planarconfiguration, and (iii) capturing the emitter membrane at the firstface using an adhesive substance.
 46. A parametric emitter array asdefined in claim 45, wherein the adhesive substance is applied to theemitter membrane to form a substantially uniform layer of adhesive onthe emitter membrane by applying the adhesive to the emitter membraneusing a screen printing technique.
 47. A parametric emitter array asdefined in claim 45, wherein the adhesive substance is applied to theemitter membrane in a layer having an average thickness of less than tenthousandths of an inch.
 48. A parametric emitter array as defined inclaim 44, further comprising a variable electrical signal applied to theemitter membrane for propagation of compression waves through theintermediate horn section and out the broad mouth opening at the secondface.
 49. A parametric emitter array as defined in claim 44, wherein theemitter membrane is coupled to the plate support member in such a waythat the film forms one of a concave and a convex surface over at leastone channel.
 50. A parametric emitter array as defined in claim 44,wherein the emitter array has a first dimension that is longer than asecond dimension to enable the emitter array to emit compression wavesthat are more directional in the first dimension compared to the seconddimension.